The four species of solitary Rugosa known from the Stony Mountain Formation at Stony Mountain in S Manitoba belong to different genera, and differ from one another in external form. The distribution and abundance of taxa and their frequency with respect to one another were related to the degree of environmental restriction. The boundary between the Gunn Member and overlying Penitentiary Member corresponds to a marked increase in overall abundance and change in relative frequency. Helicelasma and Bighornia are dominant in the Gunn and lower Penitentiary, respectively. Deiracorallium and Lobocorallium decrease in frequency at the boundary. The variable responses of these different solitary Rugosa to changes in substrate type, the influence of currents and to borers is discussed